Refractory carbonaceous linings are most commonly formed as carbon, semi-graphite or densified graphite brick. These bricks are formed by molding or pressing and firing operations. After forming, the bricks are assembled, for example, in metallurgical vessels, typically requiring long lead times from a manufacturer, highly skilled labor, and use of cutting tools to fit the brick.
Carbonaceous bricks are commonly used in operations such as blast furnace hearths to allow passage of heat to water cooling systems where conductive cooling is required. This passage of heat allows for a protective skull to form on the surface of the working lining with which the molten iron and slag can be contained. The balance of heat transfer and thermal conductivity can be maintained over long periods of time. The carbon brick is sometimes temporarily protected by the application of dense refractory brick or castable overlay of alumina and silicon carbide bearing low or no cement castables. Over time, degradation of the carbon brick lining can occur due to thermal cycling, oxidation, physical erosion, and/or attack by alkali, slag or iron, for example.
Graphite brick is typically manufactured from calcined low grade coal such as anthracite and synthetic, natural, flake or vein graphite with various additives (silicon carbide, for example). The bricks are molded under high pressure, sintered and machined to a final shape. Semi-graphite brick uses cleaner carbon sources, such as low ash containing calcined and/or semi graphitized coal (anthracite), pitch based binders and various additives for anti-oxidation and other property enhancements. Graphite brick or block is the lowest contaminant version and thus exhibits the highest thermal conductivity of these materials, typically using a higher quality, low-ash coke from petroleum sources, with pitch and phenolic resin. The graphite brick may also contain alumina, silicon carbide and other small additions of various additives.
One problem with all of these carbonaceous brick or block materials is that they require first a preforming (shaping) process, second, a heat treatment processes, and third, a milling or sizing process. Further, the bricks are often not precisely sized prior to ordering, whereby they must be cut to fit on site, adding to labor costs. These materials are expensive and to inventory enough of them for repair or reline of production vessels is an undesirable expense for the traditional customer base. This adds an additional problem with these materials, namely, the lead time required for preparation and installation. Finally, the brick must be abutted for a tight fit or mortared together, and thus, highly skilled labor is required for installation.
Carbon or graphite have also been used in other refractory applications. Graphite flake is a common base material for producing crucibles. Small amounts, typically from 1 to 3% by weight, of carbon fines and/or fine size graphite sources are commonly added to monolithic refractory castables, i.e., compositions of refractory aggregate mixed with a bonding agent which will develop structural strength and set, based on alumina and/or silicon carbide as a fine discontinuous phase filler. These additions are typically employed to modify properties such as high temperature wetting behavior or reactivity of the monolithic in classic applications, for example, blast furnace iron containment runners or foundry ladle monolithic castables.
Yamamura et al, U.S. Pat. No. 5,346,942, disclose a monolithic castable comprising refractory aggregates and novalac phenolic resin provided in an organic solvent. Often, the resin/solvent combination is considered a carcinogenic substance, banned at many commercial production facilities for environmental, health and safety reasons. In particular, high solvent levels are undesirable. Yamamura et al's system is also inconvenient as it does not cure at room temperature and thus has no strength until high temperatures are encountered.
It would therefore be advantageous to provide novel refractory materials that overcome limitations and/or disadvantages of the prior art.